Building superior layered oxide cathode via rational surface engineering for both liquid & solid-state sodium ion batteries

Abstract The key to the development of advanced sodium ion batteries (SIBs) is highly dependent on the subtle design of high-performance cathode materials. Herein, the surface stabilization of P2-type Na0.7MnO2.05 is realized by dressing up a sodium polyphosphate (NaPO3) layer via melt-impregnation process. Such ionic/electronic conducting NaPO3 nanolayer positively reinforces the electrode performance by facilitating the electron transport, stabilizing the structure, and relieving the side reaction. Compared with pristine material, the designed NaPO3 coated Na0.7MnO2.05 cathode delivers a discharge capacity of 95.5 mAh g−1 at a current density of 3 A g−1. Moreover, it shows an initial capacity of 162 mAh g−1 at 0.1 A g−1, and desired capacity retention of 82% after 200 cycles in liquid-state SIBs. Encouragingly, benefiting from the inherent ionic conduction of sodium phosphate, the surface-modified cathode also exhibits appreciable rate capability (151 mAh g−1 at 0.1 A g−1, 78 mAh g−1 at 2 A g−1) and stable cycling life with 75% capacity retention after 300 cycles at 0.1 A g−1 in solid-state SIBs.